This invention relates to a method of operating a heat pump or a thermal engine with certain chloro-fluorinated hydrocarbons used as fluids for heat transfer at relatively high temperature levels.
The necessity to recover at the best various heat discharges results in the extending use of thermodynamic cycles operated with organic fluids. The heat discharges may be upgraded, in particular, either with heat pumps producing heat at a higher thermal level, or with engine cycles vaporizing an organic fluid under pressure, expanding it in a motor with production of mechanical and/or electrical energy and then condensing it at a lower pressure (Rankine cycle).
Certain chloro-fluorinated hydrocarbons, such as those complying with the formulas CF.sub.3 --CCl.sub.2 --CF.sub.3 (F-216), CF.sub.2 Cl--CFCl.sub.2 (F-113) and CF.sub.2 Cl--CF.sub.2 Cl (F-114), have been selected up to now from the products of the trade for this use, in view of their advantageous thermodynamic characteristics.
It is recalled that the fluorinated hydrocarbons are conventionally designated by a 3-figure number (preceded by the letter F or R), according to the following code:
the first figure represents the total number of carbon atoms less one (this figure is not given when it equals zero, zero corresponding in that case to one carbon atom);
the second figure represents the total number of hydrogen atoms plus one;
the third figure represents the number of fluorine atoms.
However, the increasing use of plants for upgrading thermal discharges (heat pumps or motors) in the industry, as well as the effort to obtain improved performances, lead to the use of relatively high temperatures.
The problems to be faced are linked to the fact that the organic fluids, such as chloro-fluorinated hydrocarbons proposed up to now decompose, usually under the effect of heat and metals, in the presence of the lubricants used in the mechanical parts of the heat pumps and motors, even when these lubricants have been selected from the best synthesis products, such as, for example, olefin oligomers or certain alkylbenzenes.
It has now been found that certain chloro-fluorinated hydrocarbons have a sufficient stability for use in plants operated at high temperatures without suffering from the above disadvantages. The temperatures used are, for example, higher than 80.degree. C.